1. Field of the Invention
The present invention relates to a process for the preparation of an N-(long-chain acyl)amino acid and a process for the preparation of a salt of an N-(long-chain acyl)amino acid, and an intermediate amidonitrile and a process for the preparation thereof. More particularly, the present invention relates to a process suitable for industrial production by which an amidonitrile, N-(long-chain acyl)amino acid or a salt thereof each having a high purity can be prepared from inexpensive raw materials through simple and easy operation independently of the material of the reactor used.
2. Description of the Related Art
N-(Long-chain acyl)amino acids and salts thereof are used in various fields, because they are excellent in surface activating effect and bacteriostatic activity and are low in irritant effects.
As a process for the preparation of an N-(long-chain acyl)amino acid salt, there has hitherto been known the Schotten-Baumann reaction which comprises reacting an amino acid with a fatty acid halide in the presence of an alkali, and further several improvements of the reaction have also been proposed. Furthermore, there has also been known a reaction of converting the salt prepared by the above reaction into an N-(long-chain acyl)amino acid through double decomposition with a strong acid.
These reactions are represented by the following reaction scheme: ##STR2## wherein RCO-- represents a long-chain acyl group; and R' represents an alkylene group having 1 to 5 carbon atoms.
However, the Schotten-Baumann reaction and the improvements thereof must use, as the raw materials, an amino acid and a fatty acid halide, which are too expensive for industrial use. Further, the use of a fatty acid halide limits the material of the preparation apparatus used.
It has also been known that the quality of a fatty acid halide greatly influences the quality of the N-(long-chain acyl)amino acid prepared therefrom [see Japanese Patent Publication-A Nos. 4-321656 (published on Nov. 11, 1992) and 5-97787 (published on Apr. 20, 1993)]. Therefore, the preparation of an N-(long-chain acyl)amino acid or salt thereof each having a high quality necessitates complicated steps, disadvantageously.
Meanwhile, Shirai et al. disclosed a process for the preparation of an N-(long-chain acyl)amino acid or a salt thereof which comprises acylating an aminonitrile with an acid chloride and then hydrolyzing the obtained product [see Yuki Gosei Kagaku (Organic Synthetic Chemistry), Vol. 30, No. 1, p.p. 68-75, 1972].
However, the process of Shirai et al. also uses an acid chloride as the raw material, so that it must have disadvantages similar to those of the above Schotten Baumann reaction and improvements thereof.
Under these circumstances, it is advantageous to develop a process suitable for industrial production for preparing an N-(long-chain acyl)amino acid or a salt thereof.